As we build up light rays, the shape of the envelope begins to emerge. The only difference between this diagram and the physical system is that here, the overlap makes a dark envelope, whereas in the cup the overlap makes a bright envelope

Antigoni is a PhD student at UCL working on Boundary Element Methods for electromagnetic scattering.
More from Chalkdust
How much hair?
Thomas Sperling discusses some furry Fermi problemsBetween a square rock and a hard pentagon: fractional polygons
A polygon with four and a half sides?!Creating hot ice
We created hot ice from scratch, a solution that remains liquid even below its freezing point!Curiouser and curiouser!
Some surprising mathematical factsFind your perfect partner
Find your perfect partner with this wonderful tree diagram!Advent facts I
Santa's sack of scientific surprises